Monitoring for Equine Viral Arteritis has decreased its prevalence in European breeding sires

Abstract

Equine viral arteritis (EVA) can induce a persistent carrier state in stallions and shedding of the virus with semen can spread EVA and cause abortions in seronegative pregnant mares. In the early 1990s, obligatory testing for EVA of stallions used for artificial insemination was implemented within the European Union (Council Directive 92/65/EEC). In addition, vaccination programs for young stallions and exclusion of carrier stallions from certain breed registry events were implemented in Warmblood sport horses. Information on the efficacy of these actions on the prevalence of EVA in reproductively active stallions are not yet available in Europe. This study retrospectively analyzed results of serological and virus antigen testing for EVA in sires (n=308, one sample set per sire, EVA-vaccination status unknown) of different age and breed referred to the Centre for Artificial Insemination of Vetmeduni Vienna for semen preservation between 2001 and 2021. For analysis, stallions were grouped by age (1-3, 4-10, 11-16, >16 years) and breed. The EVA antibody titer was determined by serum neutralization test and semen was analyzed for EVA virus by PCR and/or virus isolation test. Statistical analysis was performed by chi2-test, Kruskal-Wallis test or Mann-Whitney U-test using the IBM SPSS 28.0 statistics software. Of 308 stallions tested, 14.9% (n=46) were EVA seropositive and in 12 stallions EVAvirus was detected in semen (26% of seropositive and 3.8% of all tested stallions, respectively). The incidence of seropositive stallions (22% of sires tested during 2001-05 to 4.1% during 2016-21) and of stallions shedding EVA virus via semen (8.5% of all serologically tested stallions 2001-05 to 1.4% during 2016-21) decreased over time (p<0.05). No difference among breeds with regard to occurrence of seropositive stallions was detected. There was a tendency towards more Standardbred and Lipizzaner stallions (14% and 13%, respectively) shedding EVA virus in semen compared to all other breeds (<3%, p=0.074 among groups). Differences in the seroprevalence of EVA antibodies existed among stallions from different age groups (p<0.01) with the highest percentage of seropositive stallions in 11-16 year-stallions (45.7%). No differences among age groups with regard to virus shedding existed. The EVA antibody titer increased with age (p<0.01), reflecting a higher possibility of repeated virus challenge in older stallions. Antibody titer was not associated with carrier state. In conclusion, monitoring of stallions for EVA in combination with vaccination programs resulted in a decrease of the prevalence of seropositive and virus-shedding stallions during the past 20 years in a European stallion population and can therefore be considered successful.